alias _banac {
  var %:ibo = 1
  while %:ibo <= $ibl($1,0) {
    if $calc($ctime - $ibl($1,%:ibo).ctime) >= 900 {
    var %:ban $addtok(%:ban,$ibl($1,%:ibo),32) }
    inc %:ibo
  }
  var %ss $token(%:ban,0,32)
  mode $1 $+(-,$str(b,%ss)) $token(%:ban,$+(1-,%ss),32)
}